1. Field of the Invention
The present invention relates to improvements in fabric seams, and in particular, but not exclusively to, fabric seams used in the jointing of papermachine clothing.
2. Description of the Related Art
A woven fabric for seamed papermachine clothing generally has the warp yarns at its respective transverse end faces woven back into the fabric to form loops at each of the respective fabric ends, the ends are then placed in end-to-end disposition in order to interdigitate the loops and a pintle wire is then inserted in the interdigitated loops to lock the ends together to bring the fabric into an endless form.
The region of the seam has a larger void area than the rest of the fabric, resulting in a differential dewatering in this area which may lead to marking of the paper web. Also, if the fabric is used as a base fabric in a press felt, a batt layer is needled to the base fabric, this batt being less well anchored to the fabric in the region of the seam. The void area in the region of the seam results also in a higher air permeability, which means that on passing a dewatering suction box this seam area may become more sucked therein than the rest of the fabric, thereby increasing wear in the seam region and further reducing the adherence of the batt to the base cloth. The void area will also compress more when the fabric goes through a press nip, the difference in compressibility increasing the incidence of marking of the paper web. The void areas will also allow more water flow in the press nip resulting in a hydraulic mark in the paper web.
In order to mitigate this, various methods have been tried in order to improve the wear resistance of the seam by applying scrims and adhesive treatments. However, it has been found that such treatments reduce the permeability of the belt in the region of the seam and this can lead to undesired marking of the paper web as a result of the differential dewatering in the region of the seam. Also, the treatment can add to belt stiffness. Increased stiffness and difference in permeability can each cause press bounce and render the belt more prone to filling. Also, the major problem with these methods is that of being able to locate the scrim or adhesive with precision.
Another approach to solving this problem is described in International Patent Application No. WO 92/11412 (Nordiskafilt AB) in which a multi filament yarn is woven, during the weaving of the papermachine clothing, in the loop yarns in a plain weave in order to strengthen the seam and reduce the differential permeability in the seam region. The structure formed is then exposed to a heat treatment in order to finish the papermachine clothing. The drawback to this approach is that it impedes installation of the connecting pintle wire, since the multifilament yarn is woven inside the part of the loop through which the pintle is inserted. Also, the heat setting finishing treatment precludes the use of weaving the loops with a low melt multifilament yarn, since such a yarn would melt during the heat setting process. Sewing the yarn in after heat setting is so time consuming that it makes it uneconomical to do so.
What is needed in the art is to retard the rate of seam wear and to provide more homogeneity with respect to hydraulic pressure in the seam region when compared to that of the remaining fabric.